1. Field of the Invention
This invention relates to an apparatus for detecting ultrasonic vibration, and more particularly to an apparatus comprising an iron core, a coil and a magnet surrounding a magnetic projection attached to an electrostrictive Langevin type ultrasonic vibration for detecting and feeding back voltage changes induced by the vibration of the magnetic projection and thus controlling the frequency of the vibrator.
2. Description of the Prior Art
As is well known in the art, there are two types of ultrasonic vibrators: (1) the magnetostrictive type which has the defect of generating a large amount of heat during operation and consequently needs cooling; and (2) the more prevalent electrostrictive type, among which the fixed bolt Langevin configuration is mostly used owing to its high efficiency and durability.
For maximum efficiency an ultrasonic vibrator should operate exactly at its resonant frequency, but the actual operating frequency deviates from resonance due to changes in load and working temperature. Therefore, one must detect the actual deviation from the resonant frequency and feed it back for control. To this end a pickup device with a detecting sensor, such as a ceramic element, has been attached to the vibrator to detect its frequency and restore it to the resonant frequency.
However, in such a device the measured value of the detected frequency lies below its true value because of the temperature rise during operation. This leads to a continual upward adjustment of the frequency until the excessive frequency ultimately destroys the apparatus. Two defects are apparent: the need for cooling, and the danger of the sensor itself being vibrated off or destroyed. There is thus a need for an improved detector which has none of these defects.